It is known to associate each transponder to a high power amplifier of a given power. These known payload systems have the inconvenience that the power to be transmitted by each transponder can be reduced if less power is required but cannot be increased beyond the maximum power of the amplifier. This means that the high power amplifier is dimensioned for the maximum power envisaged. Power which is not used by the high power amplifier of a transponder cannot be allocated to another one which may require extra power. The capacity of each transponder is limited by the maximum power of its high power amplifier.